In the manufacture of containers such as glass bottles and jars, various types of anomalies can occur in the sidewalls, heels, bottoms, shoulders, necks and/or finishes of the containers. These anomalies, termed “commercial variations” in the art, can affect commercial acceptability of the containers. It has been proposed to employ electro-optical inspection techniques for detecting commercial variations that affect the optical properties of the containers. The basic principle is that a light source is positioned to direct light energy onto the container, and a light sensor is positioned to receive an image of a portion of the container illuminated by the light source. An information processor is coupled to the sensor to detect commercial variations in the container as a function of the light energy received at the sensor.
Blisters can be envisioned as air pockets in a container wall, which can arise for various reasons during the container manufacturing process. It has been proposed to detect blisters in container walls by transmitting light through the container walls and detecting the blisters as a function of refraction of the light at the edges of the blisters. See U.S. Pat. Nos. 5,233,186 and 5,243,400. However, this technique can be problematic for large flat blisters, in which the edges are relatively small. It is a general object of the present invention to provide an apparatus and method for enhanced detection of blisters and/or embossments in a container wall.